Influence of non-uniformity of air flow velocity field along the frontal surface of porous objects on their aerodynamic resistance
Mathematics. Physics. Mechanics
Kurgan State University, 25, Gogolev St., Kurgan, 640669, Russia
The first part of the paper considers the hypothesis about the influence of the non-uniform air flow on the aerodynamic drag of porous objects. The aerodynamic drag of porous objects such as radiators, mesh guards and screens, aerodynamic grids and grills, etc., which are installed in the air duct, is bigger than their resistance in ideal laboratory conditions. This difference appears when the air flow with non-uniform velocity distribution along the frontal surface flows through such an object. The research allowed to establish the factors, which influence the increase in the aerodynamic drag of the porous objects. The paper presents a formula for determining the aerodynamic drag of porous objects in a non-uniform air flow. The degree of change of radiator aerodynamic drag depends on two factors: the value of air flow non-uniformity and aerodynamic characteristics of the radiator itself (these characteristics are obtained during the tests with uniform flow).
The second part of the paper analyzes the reasons for this phenomenon. To carry out this analysis a radiator was considered as a porous object example. The suggested hypothesis was verified by using a Computational Fluid Dynamics (CFD) software module. It was found that the coefficient of variation of aerodynamic resistance of porous objects depends on the curvature of the graphical representation of their aerodynamic characteristic function. The larger the curvature of the function graphical representation is, the more the object is sensitive to the non-uniformity of the air flow.
Non-uniform air flow affects the aerodynamic characteristics of the radiator. In its turn the radiator also affects the airflow. As a result of interaction with the radiator the air flow is redistributed across its cross-section. This property of the radiator is important from the point of view of its heat emission. It was established that the larger the curvature of the aerodynamic characteristic is, the better the radiator equalizes the speed of the air flow across its cross-section.
The conducted research has shown that two interconnected processes can be observed during the passage of the air flow with non-uniform velocity distribution across the channel cross-section through the porous objects. On one hand, the porous objects affect the flow, on the other hand the non-uniform flow itself affects the aerodynamic characteristics of the object. The speeds within the air flow with a non-uniform velocity distribution across the cross-section of the channel are partially equalized while passing through the porous object.
Keywords:unique distribution of velocities of the air, porous object, radiator, aerodynamic resistance
- Jong Min Choi, Payne W. Vance and Piotr A. Effects of Non-Uniform Refrigerant and Air Flow Distributions on Finned-Tube Evaporator Performance, Proceedings of International Congress of Refrigeration, Domanski National Institute of Standards and Technology, Washington, D.C., 2003, ICR-0040.
- Bury T., Kruczek T. Application of infrared thermography for validation of numerical analyses results of a finned cross-flow heat exchanger with non uniform flow of the agents, Proceedings of the 9th International Conference on Quantitative InfraRed Thermography, Krakow, Poland 2008, pp. 291-298.
- Bury T., Mitrovic Jovan. Impact of a Medium Flow Maldistribution on a Cross-Flow Heat Exchanger Performance. Heat Exchangers. Basics Design Applications, Proceedings of the International Conference on Innovative Technology (INTECH), Rijeka, Croatia, 2012, 586 p.
- Idel’chik I.E. Ajero-gidrodinamika tehnologicheskih apparatov. Podvod, otvod i raspredelenie potoka po secheniju apparatov (Aerohydrodynamics of manufacturing devices. Inlet, outlet and distribution of the flow across the cross-section of the devices), Moscow, Mashinostroenie, 1983, 351 p.
- Zajcev D.V., Sergeev S.G., Bezrukov Yu.A., Lisenkov E.A.,Uliynovskii V.N., Saliy L.A. Materialy 6 Mezhdunarodnoi conferensii MNTK «Safety Assurance of NPP with WWER» «A study of pressure loss in WWER-1500 flow path», 2009, available at: http://www.gidropress.podolsk.ru/files/proceedings/mntk2009/disc/autorun/article45-ru.htm.
- Bobkov A.V. Ocenka vlijanija frontal’nogo turbulizatora na gidravlicheskoe soprotivlenie diffuzora. Sovremennye problemy nauki i obrazovanija (Assessment of front turbulators on hydraulic resistance diffuser. Modern problems of science and education), 2012, no. 3, http://www.science-education.ru/103-6337.
- Burkov V.V. Teoreticheskoe i jeksperimental’noe issledovanie obosnovanie putej povyshenija jeffektivnosti i jekonomichnosti vodjanyh radiatorov traktorov, avtomobilej i kombajnov (Theoretical and experimental research justification of the ways to improve effectiveness and economic efficiency of water radiators of tractors, cars and combined harvesters), Doctor’s thesis, LSHI, 1968, 595 p.